Testing The Pressure Cap

TOOLS REQUIRED : Cooling System Pressure Test Adapter (J43421).

WARNING: Do not remove pressure cap from a hot system. Allow the system to cool, then slowly remove pressure cap.

NOTE: If vehicle has experienced cooling system boil over, the pressure cap must be replaced.

Remove pressure cap from coolant surge tank.

Fig 1: Removing Pressure Cap From Coolant Surge Tank
Courtesy of GENERAL MOTORS CORP.
Make sure that all parts of the pressure cap, tester, and adapter are clean.
Wet the rubber gasket of the pressure cap with water and install on the cooling system pressure test adapter.
Hold the tester with the cooling system pressure test adapter hanging straight down.

Fig 2: Operating Cooling System Pressure Test Adapter
Courtesy of GENERAL MOTORS CORP.

WARNING: Wear safety goggles.

WARNING: Never pump the pressure cap above 138 kPa (20 psi).
Pump the tester, watch pressure gauge, and read maximum pressure before relief valve opens. Stop pumping. The pressure cap is rated at 138 kPa (20 psi).
NOTE: The cap opening pressure is 86-117 kPa (13-17 psi) and the vacuum relief setting is 6.9 kPa (1.0 psi) below atmospheric pressure.
Watch needle for 30 seconds to see if it falls. The needle should not fall below 68.1 kPa (10 psi).